We thought of five props that we could use, but we also understand that 2 (the badge and the mask) could be costume and so we are omitting these from this plan. 

The first thought for a prop was the detectives badge. even though it is a part of his costume at first, we thought it would also be a prop when he uses it to open doors. The same could apply for the murderers mask.The knife, as it is the murder weapon would definitely be needed. We thought the knife would make these murders a lot closer, making it seem personal